Because they know exactly what they want. And they book Abbey Road also. And any another studio which is suitable with a purpose. They can rent even public crapper for one percussion hit. I've never heard about any home-recorded, mixed and mastered Grammy-winning song.
Two things: one, those producers don't record in a living room because it's the preferred acoustical environment. They do so because it's a different/more relaxed atmosphere that hopefully helps the artist/band give a better performance. Or because not every project they work on has the budget to book 4 weeks at Abbey Road.
Two, the notion that you can't make good recordings at home because you don't know any GRAMMY-winning examples is just absurd logic. This thread is about using tools to improve the quality of your home studio recordings, specifically vocals through the use of a reflection filter. Nobody is saying a $200 foam gadget is going to turn your bedroom into Capitol Studio A.